Influence of soil and organic residue management onbiomass and biodiversity of understory vegetation

in a Eucalyptus globulus Labill. plantation

A. Fabiao*, M.C. Martins, C. Cerveira, C. Santos,M. Lousa, M. Madeira, A. Correia

Instituto Superior de Agronomia, Tapada da Ajuda, P-1349-017 Lisboa, Portugal

Abstract

The objective of this study was to assess the effect of different options of soil preparation and management of harvesting debris on

biodiversity and biomass of understory vegetation in plantations of Eucalyptus globulus of Central Portugal. The experiment

consisted of six treatments in a replanted area and four treatments in a coppice area with five replicates, following a randomised

block design. Surveys of vegetation were performed for 6 years. The proportion of soil cover by plant species was estimated and the

Shannon–Wiener diversity and equitability indexes determined for each treatment and year. After the 2nd year, the understory

vegetation was randomly sampled for above-ground biomass determination. Within the planted area, the removal of slash without

soil preparation induced the highest number of species during the experimental period. A similar trend was observed in the coppice

area, but less regularly. Significant differences in the proportion of soil cover only occurred within the planted area in the first year,

when slash removal without soil preparation induced the highest understory cover. Species diversity was not clearly affected by

treatments: significant differences only occurred occasionally and were apparently related to differences in the number of species.

Therefore, differences in the equitability index between treatments never were significant. Removal of slash without soil

disturbance and broadcast of slash over the soil usually shared the highest biodiversity. Differences between treatments in the

amount of understory biomass were never statistically significant during the experimental period. Tendency for a negative influence

of soil mobilisation on the amount of understory biomass was observed within the planted area, as well as a similar effect of the

treatments consisting of broadcast of slash over the soil surface in the coppice area. In parallel to tree development and canopy

closure biomass of that vegetation along the study period was reduced, especially in the planted area.

# 2002 Elsevier Science B.V. All rights reserved.

Keywords: Biodiversity; Biomass; Equitability; Eucalyptus plantations; Site preparation; Understory

1. Introduction

The plantation of fast growing forest tree species

has usually been established in Portugal following

intensive site preparation, which causes deep soil dis-

turbance (with variable depths according to site char-

acteristics) and the destruction of the existing natural

vegetation (Alves, 1988). These techniques may sig-

nificantly reduce the amount of soil organic matter

(Madeira et al., 1989), and may affect the soil water

holding capacity. Planting of a fast growing tree spe-

cies may have a negative effect on the reestablishment

Forest Ecology and Management 171 (2002) 87–100

* Corresponding author. Tel.: þ351-21-365-3488;

fax: þ351-21-364-5000.

E-mail address: afabiao@isa.utl.pt (A. Fabiao).

0378-1127/02/$ – see front matter # 2002 Elsevier Science B.V. All rights reserved.

PII: S 0 3 7 8 - 1 1 2 7 ( 0 2 ) 0 0 4 6 3 - 2

of natural vegetation in the understory (Alves et al.,

1990). Frequently, understory species are good com-

petitors for the fast growing tree seedlings (Alves et al.,

1990; Smith et al., 1997).

Coppicing of forest tree plantations is almost

always performed with the use of heavy machinery

for the extraction of timber from the stand, driven by

the need to increase efficiency by reducing operation

costs. The use of heavy machinery may significantly

increase soil compaction, mainly through alterations

of the soil porosity (Lenhard, 1986). The displacement

of boles and the heavy accumulation of slash on soil

surface may also have an important negative effect on

the reestablishment and survival of the understory

vegetation (Smith et al., 1997). The consequences

resulting from reduction in understory on ecosystem

functions have been poorly studied.

After harvesting, slash may be removed from the

site to prevent fire hazard and to ease the execution of

operations during the growing stages of a stand (Smith

et al., 1997). Due to the exportation and displacement

of nutrients contained in plant biomass a negative

effect on site fertility may occur (Nyland et al.,

1979; Abbott and Crossley, 1982; Burger and Prichett,

1984; Smith et al., 1997). This may also be unfavour-

able to the reestablishment of understory vegetation

and in some situations even to the development of the

tree stratum (Smethurst and Nambiar, 1989; Emmett

et al., 1991).

Therefore, fast growing forest tree plantations—

and, in particular, those of Eucalyptus globulus Labill.

in the Iberian Peninsula—are usually considered as

having less understory vegetation than other types of

forest stands or other kinds of vegetation cover (Rosa

et al., 1986; Bernaldez et al., 1989; Alves et al., 1990).

The judgement of value on this fact is not, however,

consensual. The presence of natural vegetation is not

always desirable during the early growth stages of

planted forest seedlings due to competition for water

and nutrients, especially where prolonged seasonal

water stress is expected (Nyland, 1996; Smith et al.,

1997). On the other hand, the maintenance of the

understory plant cover guarantees protection against

soil erosion when the stand canopy is not yet closed,

and the understory contributes to the nutrient cycles

and to the stability of soil aggregation (Tisdall and

Oades, 1982). In addition, the natural plant cover

protects young seedlings against wind and frost (Smith

et al., 1997) and increases the landscape and environ-

mental value of forested areas (Crowe, 1966, 1978;

Forestry Commission, 1994). Moreover, the biodiver-

sity of understory vegetation in intensively managed

forest plantations may be an indicator for the preser-

vation of overall biodiversity and of ecological sus-

tainability (Bengtsson et al., 2000).

Within the above-mentioned context, it is of utmost

importance to identify the effects on the understory

vegetation of different methods of slash management

and soil preparation at outplanting. In addition, the

effects of slash disposal after coppice on subsequent

understory vegetation development are poorly under-

stood, recommending further research on the impact

of alternative options of organic matter management.

The aim of this study was therefore to evaluate the

effect of slash management alternatives (both in newly

established and coppice plantations) and soil prepara-

tion techniques (in new plantations) on biomass and

species diversity of understory vegetation in planta-

tions of E. globulus intensively established and man-

aged in Central Portugal. Preliminary results on

biodiversity during the early growth stage (1–3 years)

have already been published elsewhere (Cerveira et al.,

1999), and suggest a positive effect of slash disposal,

and absence or low intensity of soil disturbance, on

understory species richness.

2. Methods and materials

2.1. Site characteristics

The experiment was installed at the end of March

1993 in an E. globulus plantation at Quinta do Fur-

adouro (398200N, 98130W, 30 m.a.s.l.), in West Central

Portugal, ca. 10 km from the Atlantic Ocean. After

coppice of a previous first rotation eucalyptus planta-

tion, the stumps were killed with a systemic herbicide

in part of the area (planted area) to install a new stand

with eucalyptus seedlings from a single clone prove-

nance. In the remaining area, the stumps were allowed

to sprout and regenerate to form a new stand (coppice

area). In both areas, the tree density was kept at

approximately 1111 ha�1 (3 m � 3 m spacing). In

the planted area, each seedling was supplied at out-

planting with ca. 100 g of a fertiliser containing 14%

N, 16% P and 17% K (Jones et al., 1999).

88 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

The climate of the site is of the Mediterranean

type, tempered by an oceanic influence. At the

weather survey station at Caldas da Raınha, ca.

12 km away from the site and 70 m.a.s.l., the mean

annual temperature averages 15.2 8C, ranging from a

monthly mean of 10.4 8C in January to 19.8 8C in

August. The occurrence of minimum temperatures

below 0 8C is occasional. Mean annual rainfall is

607 mm, but less than 10% occurs between May

and September. An atmospheric humidity rate usually

higher than 80% in the morning, during summer, as

well as frequent summer fogs, contributes to reduce

the impacts of summer drought (Reis and Goncalves,

1981).

The geology of the experimental area is dominated

by Jurassic Sandstone, with fossil remains of plants

and dinosaurs (Zbyszewski and Almeida, 1960). The

soil is an Eutric Cambisol (FAO/UNESCO, 1988),

with a base saturation level higher than 50% in the

50 cm top soil layer and a pH in water ranging from

5.2 to 5.8 in 0–80 cm soil (Table 1).

2.2. Experimental design

The experimental design consisted of six treatments

in the planted area: (A) removal of slash without soil

preparation; (B) broadcast of slash without soil pre-

paration; (C) as in B, but depositing the woody debris

between the plantation rows; (D) incorporation of

slash into the soil by harrowing (�20 cm depth);

(E) removal of slash followed by harrowing; and

(F) as D followed by deep soil preparation with a

ripper (�50 cm depth).

In the coppice area, the experimental design con-

sisted only of treatments A–D, since treatments E and

F were considered as related to the establishment of

new stands and therefore not pertinent within the

context of coppice management. Within this area,

the sprouts were thinned ca. 3 years after clear-cut

and left on the site in all the treatments. This is the

usual practice in the management of eucalyptus cop-

pices in Portugal.

This experimental design was replicated in five

different blocks in both areas. Each replicate was a

plot of 30 m � 30 m, with a core of 36 trees

(18 m � 18 m) surrounded by two buffer tree rows

on each of the four sides.

2.3. Floristic surveys

The floristic surveys were performed by the quadrat

method (Kent and Coker, 1992) every spring, when the

majority of plant species were flowering, from 1994 to

1999, i.e. until the stand was 6 years old. A wooden

frame measuring 1 m � 1 m and divided by a string in

100 0:1 m � 0:1 m squares was randomly applied four

times in each treatment plot. All the plants inside the

frame were identified to the species level (occasion-

ally, some taxa were identified only to the genus, and

some to the subspecies level). The proportion of sur-

face cover of each species was carefully estimated and

recorded.

Eucalyptus seedlings from natural regeneration by

seed from the previous stand were observed and

recorded as understory vegetation whenever present

within the frame. A similar criterion was used for

other tree species seedlings, such as Pinus radiata

(natural regeneration from a neighbour stand), Lusi-

tanian oak (Quercus faginea ssp. broteroi, with natural

occurrence in the study area) and chestnut (Castanea

sativa, with some isolated trees present in the neigh-

bourhood).

Table 1

Soil characteristics of the experimental site at Quinta do Furadouroa

Depth

(cm)

Horizon Bulk density

(g cm�3)

Silt

(g kg�1)

Clay

(g kg�1)

Organic

C (g kg�1)

pH

(H2O)

Sbase

(cmolc kg�1)

Al

(cmolc kg�1)

ECEC

(cmolc kg�1)

P

(mg g�1)

K

(mg g�1)

0–20 Ah 1.47 23 161 8.8 5.24 1.84 1.90 3.74 8.6 120

20–40 Bw 1.52 25 198 7.3 5.19 2.06 1.73 3.79 11.4 69

40–60 C1 1.54 18 172 2.3 5.62 2.56 0.72 4.28 0.7 71

60–80 C2 1.63 11 130 1.7 5.81 1.83 0.53 2.36 0.7 61

a The values represent the average of six soil profiles excavated prior to the establishment of the experiment (from Jones et al., 1999)

(Sbase—sum of base cations; ECEC—effective cation exchange capacity).

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 89

2.4. Assessment of understory biomass

A wooden frame measuring 0:5 m � 0:5 m was

randomly applied four times in each treatment plot,

every spring from 1995 to 1999 (i.e. 2nd to 6th year),

for above-ground biomass sampling. All the unders-

tory plants inside the frame were collected close to the

ground and packed separately in identified plastic

bags. They were immediately oven dried in the labora-

tory at 80–85 8C and weighed.

2.5. Data handling and statistical analysis

The data from floristic surveys were compiled and

organised in an Excel data-sheet (#Microsoft) and a

list of species by year and treatment plot was obtained.

The soil cover proportion of each species (including

the proportion of uncovered soil) in each treatment

plot was averaged. The Shannon–Wiener diversity

index H and equitability index J (Begon et al.,

1996) were calculated for each treatment plot using

the proportion of soil cover by each species in relation

to total plant cover and e-base logarithms. The oven-

dry weight of understory vegetation was organised in a

similar way, expressed in an area basis and integrated

for each treatment plot.

The average number of species per treatment plot,

the proportion of plant cover to total sampling area,

the Shannon–Wiener diversity and equitability

indexes and the total understory biomass were statis-

tically compared between treatments. The SAS-Sys-

tem for Windows, version 6, software SAS/STAT

(SAS Institute, 1989) was utilised for those compar-

isons. The normality of variance was verified by the

Kolmogorov–Smirnov test and the homogeneity was

verified through graphics of residuals (studentised

residuals � predicted values) to analyse the homose-

dasticity of residuals and their normality. The demon-

strative graphics are not shown here. Whenever the

normality and homogeneity were confirmed, the com-

parisons were performed through the procedure GLM

(generalised linear model) and the Tukey test. Blocks

and treatments were considered as the independent

variables and the average number of species, propor-

tion of soil cover, diversity and equitability indexes,

and biomass, the dependent variables. When variance

was not normal and/or the homogeneity of residuals

was not confirmed, the NPAR1WAY procedure of the

same software was used and the averages were com-

pared through the Kruskal–Wallis test. The signifi-

cance level of 0.05 was utilised in all the statistical

analysis of data. Homologous treatments of planted

Table 2

Average number of understory species in various treatment plots in the planted and coppice areasa

Years Treatments

A B C D E F

Planted area

1994 13.4a 9.0a,b 10.0a,b 10.4a,b 10.4a,b 7.6b

1995 9.4 6.8 7.4 7.4 7.6 6.6

1996 9.0 7.6 8.2 7.0 7.6 8.8

1997 14.4 10.6 10.8 10.4 12.0 11.6

1998 16.2 12.4 11.6 10.8 16.2 12.0

1999 9.0 7.4 9.0 6.2 7.8 6.2

Coppice area

1994 12.6a 6.4b 6.6b 9.6a,b – –

1995 8.0a 4.6b 5.6a,b 5.4b – –

1996 7.6a,b 3.8c 4.8b,c 8.2a,b – –

1997 13.8 12.4 10.0 9.2 – –

1998 14.6 11.2 12.4 11.6 – –

1999 11.4a 9.8a,b 8.6b 10.4a,b – –

a The values followed by different characters in the same line were statistically different (P < 0:05, GLM procedure and Tukey test).

Treatments are: (A) removal of slash and plantation without soil disturbance; (B) broadcast disposal of slash and plantation without soil

disturbance; (C): as in B, but with woody slash concentrated between the plantation rows; (D) incorporation of slash into the soil by harrowing;

E: removal of slash followed by harrowing; F: as D followed by deep soil ripping.

90 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

and coppice areas were compared using similar sta-

tistical methods.

3. Results and discussion

3.1. Number of species

The mean total number of species per treatment plot

was usually highest in the treatment A (slash removal

without generalised soil disturbance), both in planted

and coppice areas (Table 2). Within the planted area,

however, significant differences only occurred in the

first year, when treatment F (incorporation of slash

into the soil by deep ripping) had an average number

of species significantly lower than treatment A, with

the remaining treatments ranking between those two.

Within the coppice area the treatment A had a

significantly higher number of species than B and C

(broadcast of slash over the soil surface, respectively

Fig. 1. Proportion of soil covered by the three more abundant understory species during different years and in different treatments. Left:

planted area (A–F); right: coppice area (A–D). Treatments A–F are given in Table 2. HL: H. lanatus; OP: Ornithopus pinnatus; RU: R.

ulmifolius; LR: Lepidophorum repandum; CB: Conyza bonariensis; PA: P. aquilinum; AC: Agrostis curtisii; LP: Lonicera periclymenum; EG:

E. globulus; BS: Brachypodium sylvaticum; LYP: Lythrum portula; GT: Genista triacanthos; ULE: Ulex europaeus; GF: Gaudinia fragilis;

FH: F. hygrometrica; DV: Dittrichia viscosa; UM: U. minor; HH: Hedera helix; QC: Q. coccifera.

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 91

without and with woody slash concentrated between

plantation rows) in the first year, and higher than

treatments B and D (incorporation of slash into the

soil by harrowing) in the second. A low value also

occurred in the 3rd year in treatment B, but the highest

number of species was observed in treatment D,

although its value was not significantly different from

that in treatment A (cf. Table 2). The treatment A kept

the highest score from the 4th to the 6th year, but

significant differences only occurred in the latter year,

when the treatment C had the lowest number of

species.

In an experiment of slash management after harvest

performed in coniferous forests of north-western Uni-

ted Sates (site characteristics and treatments described

by Zabowski et al., 2000), Scherer et al. (2000) found

little variation in the number of species among treat-

ment plots, but marked differences in species compo-

sition. The treatment consisting of slash disposal over

the soil surface had the lowest number of species 3

years after harvest and the dominant understory spe-

cies were substantially different from those in other

treatments or in non-harvested adjacent forest.

Although our experiment is hardly comparable with

that described above, due to differences in site char-

acteristics, main forest species and silvicultural tech-

niques, we found indications of a negative influence of

the presence of slash on the number of species within

the coppice area. Differences in species composition

among treatments, however, were not apparent during

the first 4 years, neither in the planted nor in the

coppice area. The proportion of understory soil cover,

not accounting for bare soil, was usually dominated

(�60 to more than 90%) in all treatments by the three

species that ranked first in the rank-abundance dia-

grams (not shown in this article), along the study

period (Fig. 1). The grass coloniser Holcus lanatus

was dominant in almost all the treatments of both

planted and coppice areas along the first 4 years,

except for treatments A, C and D of the coppice in

the 3rd year. From the 4th year onwards a moss,

Funaria hygrometrica, became one the most abundant

species in almost all the treatments of both areas,

being strongly dominant in treatments B, D and F

(planted area) and A, B and C (coppice area) in the 5th

year. In the 6th year, F. hygrometrica ranked first in

treatments B, C, D and F (planted area) and B and C

(coppice area) suggesting a relationship with the pre-

sence of slash, either distributed over the soil, or

incorporated into the topsoil by harrowing or deep

soil ripping. Its presence in treatments consisting of

slash removal (A and E) was, however, still important

and that relationship was not clear. The change in

species composition might also be a consequence of

environmental changes at the understory level due to

canopy closure after the 4th year, as discussed below.

In some treatments of both areas, woody perennials

strongly increased their relative importance during the

6th year. Genista triacanthus (treatment D of the

planted area), Ulex minor (treatments E and F of

the same area), U. europaeus (A, coppice area), Quer-

cus coccifera (A and C, coppice area) and Rubus

ulmifolius (C and D, both areas) are good examples

of such a tendency.

Bracken (Pteridium aquilinum) was the second

most abundant species in treatment D of the coppice

area in the first 2 years, and in treatment A in the 2nd

year. It dominated in the understory plant cover of A

and D during the 3rd year (when it ranked second in

treatment C), to decrease again in the 4th (Fig. 2).

Until the end of the experiment it never was within the

three most abundant species in treatment B (broadcast

of slash over the soil surface) of the coppice area,

neither an important species in the planted area (cf.

Fig. 1). Dolling (1999) studied bracken in hemiboreal

forests of southern Sweden and concluded that this

species was suppressed under closed canopy, but the

rhizomes could survive for several years. The presence

of intact rhizomes may be the key factor for its

spreading after clear-cutting or in forest clearings,

as it apparently happened in our experiment after

coppice. The proportion of soil cover by bracken in

treatment D, where this species was abundant since the

beginning, increased with time, suggesting that the

incorporation of slash into the soil by harrowing might

have positively affected its survival and subsequent

spreading. The removal of organic soil layers and the

absence of soil disturbances in treatment A also had a

positive effect on the spreading of bracken until the

3rd year, but its importance decreased after that, in

apparent agreement with the above-mentioned sup-

pression due to canopy closure.

The coppice area usually had a lower number of

understory species than the planted area, but an inverse

situation occasionally occurred in all treatments

from the 3rd year onwards. Significant differences

92 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

between these areas only occurred in treatment C in

the first year and in treatment D in the 2nd and 6th

years, in the latter year with the highest number of

species in the coppice area.

The average number of species followed the same

general trend over the experimental period, irrespec-

tive of treatment or area, planted or coppice (Table 2).

This is in agreement with Moore and Allen (1999),

who stated that the richness of understory species in

forest plantations did not usually decrease as a con-

sequence of management practices, at least prior to

crown closure. Our results also suggest that the num-

ber of species present in the understory vegetation

reflected, at least partially, the scarcity or abundance

of winter and spring rainfall in different years, with the

highest scores in the rainy years and the lowest in the

dry ones. The experimental area in 1993–1994, 1995–

1996 and 1997–1998 received an amount of winter

and spring rainfall higher than the 50-year average

1941–1990, whereas 1994–1995 and 1998–1999

hardly totalled more than half that average (Francisco

Abreu, pers. commun.). Spring rainfall (March–May)

in 1995 was less than half the 50-year average. We

may speculate that the 1994–1995 drought may have

contributed to a decrease in the number of species in

the 2nd and 3rd years of the experiment, although the

latter had a high amount of rainfall. The recovery of

species richness in 1997 and 1998 was paralleled with

normal and high rainfall in 1996–1997 and 1997–

1998. The decrease in the number of species observed

in 1999, a dry year, may also be dependent on changes

due to stand development.

The results also suggest that species richness was

affected by the intensity of the initial perturbations

resulting from tree harvest, slash disposal, and/or soil

preparation (the latter mainly within the planted area).

In the planted area, the lowest number of species was

always observed in treatments consisting of incorpora-

tion of slash into the soil, both by surface harrowing

(treatment D, during the 3rd to 6th year period) and

deep ripping (treatment F, in the 1st, 2nd and 6th

years).

In the coppice area the treatment D had the highest

number of species in the 3rd year. The lowest score

only occurred in this treatment in the 4th year, when

species richness was exceptionally high in all the

treatments of both areas (probably as a consequence

of abundant rainfall in spring). On the other hand,

the treatments consisting of distribution of slash over

the soil surface usually had the lowest number of

species, and frequently differences were statistically

significant in relation to treatment A and/or D.

Fig. 2. Proportion of soil covered by bracken (P. aquilinum) in treatments of the coppice area along the experimental period. Treatments A–D

are given in Table 2.

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 93

This different pattern between coppice and planted

areas may have resulted from differences in tree cover

and management techniques. Early tree growth was

faster in the coppice than in the planted area (Jones

et al., 1999), and in the former the sprouts were

thinned and abandoned over the soil in all the treat-

ments between the 3rd and 4th years.

3.2. Proportion of soil cover

Within the planted area, the lowest proportions of

understory plant cover were observed in treatments C

(1st to 4th years), F (consisting of incorporation of

slash by ripping, in the 5th year) and E (removal of

slash followed by harrowing, in the 6th year) (Table 3).

The observed differences were statistically significant

only in the 1st year, with treatments A and E (con-

sisting of removal of slash, respectively without and

with soil disturbance) being significantly different

from C (consisting of broadcast of leaf and bark

residues left on the soil surface).

The differences between treatments were not sig-

nificant for the coppice area, but treatment B had the

lowest values between the 1st and the 5th years and

treatment D in the 6th. In the first year, the treatment D

had the highest proportion of understory vegetation

cover, but the difference to treatment Awas negligible.

Treatment A ranked the first between the 2nd and 4th

years, but decreased after that, ranking below treat-

ments D and C in the 5th year and below C in the 6th,

when the experiment finished.

The coppice area consistently showed lower pro-

portion of understory vegetation cover than the

planted area during the first 3 years of the experiment

(cf. Table 3). Such differences were statistically sig-

nificant (P < 0:05) in treatment A in the first 2 years,

in treatment B in the first 3 years and in treatment D in

the 2nd year. Although not significant in the 4th to 6th

years, treatments A and B kept those differences

during the experiment period. The treatment C, how-

ever, had higher soil cover in the coppice than in the

planted area from the 4th to the 6th year, and treatment

D in the 5th and 6th years (with a very small difference

in the latter year), but these differences were not

statistically significant (P > 0:05).

The treatment A usually had the highest proportion

of understory plant cover in both areas. The exceptions

occurred in the 4th year in the planted area (when

treatment F had the highest value, followed by D and

A). In the 1st and 5th years in the coppice area, the

highest values were in treatment D, and in 6th year in

treatment C.

Table 3

Average proportion (% of total area, including uncovered soil) of understory plant cover in treatment plots in the planted and coppice areasa

Years Treatments

A B C D E F

Planted area

1994 95.4a 72.9a,b 51.1b 70.0a,b 95.0a 82.0a,b

1995 93.7 88.9 53.1 78.0 81.2 82.3

1996 71.2 65.9 56.2 61.8 67.7 71.0

1997 96.75 95.55 80.65 99.15 83.90 105.75

1998 91.68 65.18 48.33 55.45 42.58 39.39

1999 87.05 62.20 63.10 39.60 26.8 40.00

Coppice area

1994 52.7 26.4 42.5 54.1 – –

1995 51.7 32.7 51.5 43.7 – –

1996 56.8 20.2 55.9 49.1 – –

1997 91.30 77.90 88.25 82.00 – –

1998 60.26 41.40 62.06 65.10 – –

1999 59.81 58.02 66.70 40.18 – –

a The values of the planted area followed by different characters in the same line were statistically different (P < 0:05, GLM procedure and

Tukey test). The differences between treatments of the coppice area were not statistically significant (P > 0:05, NPAR1WAY procedure).

Treatments are given in Table 2.

94 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

Usually a decrease in understory plant cover should

be expected after canopy closure, eventually occurring

together with a change in species composition

(Nyland, 1996; Spies, 1997; Barnes et al., 1998;

Brokaw and Lent, 1999). Yorks and Dabydeen

(1999) observed a decline in understory cover follow-

ing clear-cut in hardwood mixed forests of Maryland,

USA. The canopy closure in E. globulus plantations

may result in a sudden decrease in crown depth

(increasing the extension of bare stem), and a stabi-

lisation in the leaf area index (LAI) (Pereira et al.,

1997). In our experiment, this occurred approximately

in the 4th year, as expected in E. globulus plantations

in moderate to good quality sites in Portugal (Pereira

et al., 1997). The thinning of sprouts in the coppice

area did not delay the canopy closure, since the

remaining stems had a very fast growth response

following thinning.

Despite the qualitative changes that occurred in

understory species composition between the 4th and

5th years, a clear decrease in vegetative cover with

stand development was not observed in this experi-

ment. On the contrary, almost all the treatments had

the highest cover in the 4th year, i.e. about the canopy

closure stage (Table 3). The exception was treatment

E of the planted area, which had the highest propor-

tion of plant cover in the 1st year. The plant cover

increase in the 4th year may result from either spring

rainfall above the local average, or the high contribu-

tion of F. hygrometrica and bracken to understory

cover. The small vertical growth of F. hygrometrica

contrasts with its wide horizontal spreading, leading

to the development of a very low continuous moss

stratum over the soil. Bracken, on the other hand,

formed a higher stratum that frequently allowed the

development of other herbaceous plants under its

cover.

3.3. Shannon–Wiener diversity and equitability

indexes

Within the planted area, the relationship between

treatments on Shannon–Wiener diversity index was

not clear (Table 4). Significant differences between

treatments only occurred in the 1st and 4th years. In

the 1st year, treatments D and E had higher diversity

than treatment B, with A, C and F scoring inter-

mediate values. In the 4th year, treatment A had a

significantly higher Shannon–Wiener diversity index

than treatment E, and all the other treatments ranked

between those two. In the other years, the highest

value was in treatments A (2nd year), C (3rd and 5th

years) and E (6th year), defying any attempt of

interpretation.

In the coppice area, a difference similar to that

observed in the planted area occurred in the 4th year,

but between treatments A and D. The latter ranked as

the second lowest in the planted area in the same year,

but the difference to treatment A was not statistically

significant. The differences between treatments of the

coppice area were not significant in other years.

Treatment A usually ranked the highest index values

in all years except the 3rd and 6th year, when treatment

D scored the highest Shannon–Wiener diversity

indexes. The lowest value for diversity was in treat-

ment D in the 1st, 2nd and 4th years, in treatment B in

the 3rd year, and in treatment C in the 5th and 6th year.

With the exception of treatment C and sometimes of

treatment D, there was a tendency for higher values of

the diversity index in the coppice than in the planted

area, but the difference was significant only for treat-

ment A in the 2nd year (P < 0:05). In contrast, treat-

ment C had a Shannon–Wiener diversity index

significantly higher in the planted than in the coppice

area in the 5th year (P < 0:01). Treatment C had a

higher diversity index in the planted than in the

coppice area in the 1st, 3rd and 6th years, and the

treatment D in the 1st year, but the differences were

not significant.

Most of the differences in the diversity index may

probably be related to differences in the average

number of species in each treatment and in each year.

The differences between treatments in the equitability

index (Table 5) were never significant, either in the

planted or in the coppice areas. The highest values in

the planted area were observed in treatments E (1st

and 6th years), C (2nd, 3rd and 5th years) and A (4th

year). In the coppice area, treatment A ranked the

highest value in the 1st, 2nd and 4th years, but in other

years the maximum was shared between treatments C

(3rd year), D (5th year) and B (6th year).

With the exception of treatment D in the 1st year

(not significantly different) and C in the 5th year

(P < 0:05) and 6th years (not significantly), the cop-

pice area always had higher Shannon–Wiener equit-

ability indexes than the planted area. However, the

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 95

differences only were significant for treatment A in the

2nd year (P < 0:05), similar to that observed in the

diversity index.

Moore and Allen (1999) stated that, in intensively

managed forest plantations, complete removal of

canopy through harvesting produces a more diverse

flora than that occurring under a closed canopy. Site

preparation activities tend to reduce diversity in the

short term, but the duration of that impact depends on

the intensity of those practices. In our experiment, we

expected some kind of temporal trend in diversity of

understory vegetation, even if differences among

treatments were not clear or merely speculative. Both

diversity and equitability decreased from the first to

Table 4

Shannon–Wiener diversity index in treatment plots in the planted and coppice areasa

Year Treatments

B C D E F

Planted area

1994 1.082a,b 0.695b 1.210a,b 1.259a 1.254a 0.941a,b

1995 0.784 0.514 0.751 0.475 0.295 0.307

1996 0.949 0.580 1.027 0.785 0.828 0.848

1997 1.106a 0.751a,b 0.716a,b 0.679a,b 0.608b 0.766a,b

1998 1.293 1.047 1.559 1.120 1.407 0.959

1999 0.926 0.747 1.205 0.777 1.213 0.663

Coppice area

1994 1.549 1.092 1.119 1.082 – –

1995 1.171 0.745 0.900 0.740 – –

1996 1.054 0.627 0.804 1.287 – –

1997 1.138a 1.039a,b 0.787a,b 0.740b – –

1998 1.531 1.355 1.241 1.361 – –

1999 1.321 1.350 0.933 1.352 – –

a The values followed by different characters in the same line were statistically different (P < 0:05, GLM procedure and Tukey test).

Treatments are given in Table 2.

Table 5

Shannon–Wiener equitability index in treatment plots in the planted and coppice areasa

Year Treatments

A B C D E F

Planted area

1994 0.424 0.331 0.526 0.537 0.546 0.461

1995 0.359 0.275 0.384 0.231 0.156 0.159

1996 0.470 0.294 0.495 0.457 0.420 0.403

1997 0.422 0.314 0.306 0.298 0.248 0.315

1998 0.471 0.456 0.651 0.460 0.502 0.391

1999 0.438 0.345 0.550 0.416 0.599 0.377

Coppice area

1994 0.617 0.588 0.611 0.490 – –

1995 0.578 0.486 0.560 0.433 – –

1996 0.533 0.471 0.542 0.622 – –

1997 0.438 0.416 0.361 0.335 – –

1998 0.570 0.569 0.497 0.597 – –

1999 0.546 0.588 0.438 0.578 – –

a The differences between treatments were not statistically significant (P > 0:05, GLM procedure). Treatments are given in Table 2.

96 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

the 2nd year and in some treatments the 3rd or the 4th

year, either in planted or in coppice area, but there was

a clear increase in the 5th year in all treatments and

areas (Tables 4 and 5). This temporal pattern does not

match with any defined temporal trend in flora com-

position. Yorks and Dabydeen (1999), who studied

understory diversity in second-growth hardwood for-

ests of Maryland, USA, also found an overall absence

of any significant trend in diversity with stand age.

Apparently, differences in environmental characteris-

tics such as aspect and the dominance of single

understory species in particular sites had greater

influence in diversity than the stand age. Dominance

of the understory cover by a small number of species

Fig. 3. Variation over time of the understory biomass from the 2nd to the 6th year of the experiment in the treatments of the planted (top) and

coppice (bottom) areas. The vertical bars represent �1S.E. The differences between treatments were not statistically significant (P > 0:05,

NPAR1WAY procedure). Treatments A–F are given in Table 2.

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 97

was also observed in our study in all treatments and

both experimental areas.

Removal of slash followed by deep soil distur-

bance is probably the most common technique of site

preparation to establish eucalypt plantations in Por-

tugal. It has been demonstrated that intensive soil

preparation is not always needed for plantation suc-

cess or for wood production optimisation (Madeira

et al., 1989). The current experiment showed that tree

growth was not significantly affected by treatments

on this site (Jones et al., 1999). It may be therefore

possible to decrease the intensity of site preparation

in favourable environmental situations, for adequate

development of understory biodiversity and for wood

production.

3.4. Biomass

The understory biomass generally decreased during

the experimental period in all treatments, both in the

planted and coppice areas, but the decrease was less

regular in the latter. In most treatments, however, there

was a small increase between the 5th and the 6th year,

especially within the planted area (Fig. 3). Therefore,

the variation of understory biomass with stand age

matched the expected pattern of decline over time,

following stand development from establishment to

canopy closure. The particular development pattern of

F. hygrometrica on the proportion of understory plant

cover was not found in the biomass, due to the

negligible contribution of F. hygrometrica to the total

understory biomass.

Differences in biomass between treatments were

not significant, neither in the planted nor in the

coppice areas. Within the planted area, the lowest

biomass occurred in one of the treatments consisting

of some type of soil disturbance (D and E, by harrow-

ing, respectively with and without incorporation of

slash, and F, by ripping). The only exception was

treatment C, which scored the lowest value in the

2nd year. The highest understory biomass was always

found in treatment A (2nd and 4th to 6th years) and,

exceptionally, in treatment B (3rd year, when treat-

ment A ranked the third).

Within the coppice area the highest understory

biomass was found in treatments A (3rd, 4th and 6th

years) or D (2nd and 5th years) and the lowest

consistently in treatment B. This pattern differed

from that shown by the treatments of the planted

area, where treatment B also ranked the lowest of

treatments A–D (i.e., excluding treatments E and F),

but only during the last 3 years of the experimental

period.

The biomass data suggest that broadcast disposal

of slash over the soil surface might have inhibited the

development of understory vegetation in the coppice

area, especially when woody biomass components

(branches and twigs) were also included. A possible

reason for that inhibition might have been soil

shading by woody slash disposal. It may be specu-

lated, however, whether competition for nitrogen

between understory vegetation and decomposing

woody debris could also have an effect on the

development of understory biomass (M.C. Magal-

haes, pers. commun.). Within the planted area, as

referred above, it was soil disturbance that appar-

ently had the highest contribution to a decrease of

understory biomass, but in the last 3 years of the

experimental period treatment B also ranked the last

of treatments A–D.

4. Conclusions

The mean total number of species per treatment plot

was high when slash was removed without soil dis-

turbance, both in planted and coppice areas. This trend

was clearer for the coppice than the planted area. In the

planted area, incorporation of slash into the soil, with

or without subsoil disturbance, induced the lowest

number of species. This trend, however, was not

observed in the coppice area.

Decrease in species richness during the early stage

of stand growth followed drought conditions, both

during the year and in spring. The highest proportion

of understory plant cover was promoted when slash

was removed without soil disturbance, both in planted

and coppice areas.

The Shannon–Wiener diversity and equitability

indexes did not show a clear relationship with treat-

ments. The diversity and, especially, equitability index

were higher in the coppice than in the planted area.

Understory biomass decreased with time in the

planted area during the first 5 years of the experiment.

This decrease was not observed in the coppice area.

Broadcast distribution of slash on the soil surface

98 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100

negatively affected understory biomass in coppice

area. Data at the end of the experimental period

suggest that the development of shrubs may be respon-

sible for changes in the understory biomass.

Acknowledgements

The experiment was funded by EU (Project CEC

AIR-CT-92-0492), JNICT/FCT, Portugal (Projects

PDGT/FER/366/94 and PRAXIS XXI 3/3.2/FLOR/

2123/95), and PAMAF Program (Ministry of Agricul-

ture), Portugal (Project 4029/95). Maria do Ceu Mar-

tins, Claudia Cerveira and Conceicao Santos were

granted, as graduation students and/or junior scien-

tists, by JNICT/FCT. The pulp company Celulose

Beira Industrial (CELBI), S.A., landowner of Quinta

do Furadouro, supervised the management of the

experimental area. The contribution of two anon-

ymous referees to the improvement of the manuscript

is gratefully acknowledged.

References

Abbott, D.T., Crossley Jr., D.A., 1982. Woody litter decomposition

following clear-cutting. Ecology 63, 35–42.

Alves, A.A.M., 1988. Tecnicas de Producao Florestal. Fundamen-

tos, Tipificacao e Metodos, 2a edicao. Instituto Nacional de

Investigacao Cientıfica, Lisboa.

Alves, A.A.M., Pereira, J.M.S., Borges, J.G.C., Borges, G.C.,

Carvalho, P.O., David, J.S., Goncalves, J.H.C., Madeira, M.,

Onofre, N., Valente, F., 1990. Impactes Ambientais e Socio-

Economicos do Eucaliptal em Portugal. Departamento de

Engenharia Florestal, Universidade Tecnica de Lisboa, Instituto

Superior de Agronomia, Lisboa.

Barnes, B.V., Zak, D.R., Denton, S.R., Spurr, S.H., 1998. Forest

Ecology, 4th ed. Wiley, New York.

Begon, M., Harper, J.L., Townsend, C.R., 1996. Ecology, 3rd ed.

Blackwell Science, Oxford.

Bengtsson, J., Nilsson, S.G., Franc, A., Menozzi, P., 2000.

Biodiversity, disturbances, ecosystem function and manage-

ment of European forests. For. Ecol. Manage. 132, 39–50.

Bernaldez, F.G., Perez, R.P., Levassor, C., 1989. Effets des

Plantations d’Eucalyptus dans le Nord d’Espagne. Commission

des Communautes Europeennes, Brussels.

Brokaw, N.V., Lent, R.A., 1999. Vertical structure. In: Hunter Jr.,

M.L. (Ed.), Maintaining Biodiversity in Forest Ecosystems.

Cambridge University Press, Cambridge, pp. 373–399.

Burger, J.A., Prichett, W.L., 1984. Effects of clearfelling and site

preparation on nitrogen mineralization in a southern pine stand.

Soil Sci. Soc. Am. J. 48, 1432–1437.

Cerveira, C., Lousa, M., Fabiao, A., Madeira, M., Tome, M., 1999.

Influencia de tecnicas de instalacao e conducao do eucaliptal na

diversidade da vegetacao sob coberto. Revista de Ciencias

Agrarias XXII (2), 49–63.

Crowe, S., 1966. Forestry in the Landscape. Forestry Commission

Booklet No. 18. Her Majesty’s Stationery Office, London.

Crowe, S., 1978. The Landscape of Forests and Woods. Forestry

Commission Booklet No. 44. Her Majesty’s Stationery Office,

London.

Dolling, A., 1999. The vegetative spread of Pteridium aquilinum in

a hemiboreal forest—invasion or revegetation. For. Ecol.

Manage. 124, 177–184.

Emmett, B.A., Anderson, J.M., Hornung, M., 1991. Nitrogen sinus

following two intensities of harvesting in a Sitka spruce forest

(N. Wales) and the effect on the establishment of the next

cropping. For. Ecol. Manage. 41, 81–93.

FAO/UNESCO, 1988. Soil Map of the World (revised legend).

FAO, Rome.

Forestry Commission, 1994. Forest Landscape Design Guidelines.

Her Majesty’s Stationery Office, London.

Jones, H.E., Madeira, M., Herraez, L., Dighton, J., Fabiao, A.,

Gonzalez-Rio, F., Fernandez-Marcos, M., Gomez, C., Tome,

M., Feith, H., Magalhaes, M.C., Howson, G., 1999. The effect

of organic matter management on the productivity of

Eucalyptus globulus stands in Spain and Portugal: tree growth

and harvest residue decomposition in relation to site and

treatment. For. Ecol. Manage. 122, 73–86.

Kent, M., Coker, P., 1992. Vegetation Description and Analysis: A

Practical Approach. Belhaven Press, London.

Lenhard, R.J., 1986. Change in void distribution and volume during

compaction of a forest soil. Soil Sci. Soc. Am. J. 50, 462–

464.

Madeira, M., Melo, G., Alexandre, C., Steen, E., 1989. Effects of

deep ploughing and superficial disc harrowing on physical and

chemical soil properties and biomass in a new plantation of

Eucalyptus globulus. Soil Till. Res. 14, 163–175.

Moore, S.E., Allen, H.L., 1999. Plantation forestry. In: Hunter Jr.,

M.L. (Ed.), Maintaining Biodiversity in Forest Ecosystems.

Cambridge University Press, Cambridge, pp. 400–433.

Nyland, R.D., 1996. Silviculture: Concepts and Applications.

Forestry Series. McGraw-Hill, New York.

Nyland, R.D., Leaf, A.L., Bickelhaut, D.H., 1979. Litter removal

impairs growth of direct seeded Norway spruce. For. Sci. 25,

244–246.

Pereira, J.M.C., Tome, M., Carreiras, J.M.B., Tome, J.A., Pereira,

J.S., David, J.S., Fabiao, A.M.D., 1997. Leaf area estimation

from tree allometrics in Eucalyptus globulus plantations. Can.

J. For. Res. 27, 166–173.

Reis, R.M., Goncalves M.Z., 1981. Caracterizacao Climatica da

Regiao Agrıcola do Ribatejo e Oeste. O Clima de Portugal.

Fasc. XXXII. Instituto Nacional de Meteorologia e Geofısica,

Lisboa.

Rosa, M.L., Gomes, M.F., Espırito-Santo, M.D., 1986. Influencia

de factores ecologicos e fitotecnicos na Flora espontanea de

sistemas florestais da regiao de Castelo Branco. In: 1 Congresso

Florestal Nacional. Fundacao Calouste Gulbenkian, Lisboa,

pp. 255–260.

A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100 99

SAS Institute, 1989. SAS/STAT User Guide, vol. II, Version 6, 4th

ed. SAS Institute, Cary, NC.

Scherer, G., Zabowski, D., Java, B., Everett, R., 2000. Timber

harvesting residue treatment. Part II. Understory vegetation

response. For. Ecol. Manage. 126, 35–50.

Smethurst, P.J., Nambiar, E.S.K., 1989. Role of weeds in the

management of nitrogen in a young Pinus radiata plantation.

New For. 3, 203–224.

Smith, D.M., Larson, B.C., Kelty, M.J., Ashton P.M.S., 1997. The

Practice of Silviculture: Applied Forest Ecology, 9th ed. Wiley,

New York.

Spies, T., 1997. Forest stand structure, composition and

function. In: Kohm, K.A., Franklin, J.F. (Eds.), Creating a

Forestry for the 21st Century: The Science of Ecosy-

stem Management. Island Press, Washington, DC, pp. 11–

30.

Tisdall, J.M., Oades, J.M., 1982. Organic matter and water stable

aggregates in soils. J. Soil Sci. 33, 141–163.

Yorks, T.E., Dabydeen, S., 1999. Seasonal and successional

understory vascular plant diversity in second-growth hardwood

clearcuts of western Maryland, USA. For. Ecol. Manage. 119,

217–230.

Zabowski, D., Java, B., Scherer, G., Everett, R.L., Ottmar, R., 2000.

Timber harvesting residue treatment. Part I. Responses of conifer

seedlings, soils and microclimate. For. Ecol. Manage. 126, 25–34.

Zbyszewski, G., Almeida F.M., 1960. Carta Geologica de Portugal

(Esc. 1:50 000). Notıcia Explicativa da Folha 26-D. Servicos

Geologicos de Portugal, Lisboa.

100 A. Fabiao et al. / Forest Ecology and Management 171 (2002) 87–100